1. Field of the Invention
The present invention relates to a swash plate compressor used for a vehicle air-conditioning system etc.
2. Description of the Related Art
A refrigeration circuit used in a vehicle air-conditioning system includes a compressor for compressing a refrigerant gas. This compressor comes in various forms such as variable displacement types and fixed displacement types. More specifically, fixed displacement type compressors include not only single-headed piston type swash plate compressors, but also double-headed piston type swash plate types. Variable displacement type compressors also include not only single-headed piston type swash plate compressors, but also double-headed piston type swash plate compressors.
Among these compressors, a general swash plate compressor defines and forms, inside its housing, cylinder bores, a crank chamber, a suction chamber, and a discharge chamber. Each cylinder bore accommodates a piston so that it may reciprocate. Further, a drive shaft supported rotatably by the housing is driven by an engine or another external drive source. The swash plate is supported to be able to synchronously rotate with respect to the drive shaft. A pair of shoes is accomodated in a pair of shoe seats provided at an engagement portion in the piston to drive the pistons and is provided at the front and rear of the swash plate.
If the swash plate is inclined at a certain angle with respect to the drive shaft, the compressor is a fixed displacement swash plate compressor. If the inclination angle of the swash plate is variable with respect to the drive shaft and the pressure in the crank chamber can be adjusted by a control valve to change the inclination angle and adjust the discharge capacity, the compressor is a variable displacement swash plate compressor. On the other hand, if the piston is a single-headed piston having a head at only one of the front and rear of the swash plate, the compressor is a single-headed piston type swash plate compressor. If the piston is a double-headed piston having heads at both the front and rear of the swash plate, it is a double-headed piston type swash plate compressor.
In this swash plate compressor, if the drive shaft is driven by an external drive source, the swash plate synchronously rotates, so the pistons reciprocate in the cylinder bores through shoes. Due to this, each cylinder bore forms a compression chamber with the head of the piston, so when the piston is in the suction stroke, low pressure refrigerant gas is sucked by the piston from the suction chamber connected to an evaporator of the refrigeration circuit. When the piston is in the compression stroke, high pressure refrigerant gas is discharged to the discharge chamber from the compression chamber. This discharge chamber is connected to a condenser of the refrigeration circuit. The refrigeration circuit is used as a vehicle air-conditioning system for air-conditioning a vehicle. During this time, in the swash plate compressor, the slidability of the sliding portions between the swash plate and the shoes is ensured by a mist of lubricating oil contained in the refrigerant gas.
In the above swash plate compressors of the related art, however, the shoes were mainly comprised of a ferrous material, such as SUJ2 according to Japan Industrial Standards (JIS), and had the disadvantage that they were heavy. This disadvantage was present in both fixed displacement swash plate compressors and variable displacement swash plate compressors. Further, it similarly was present in single-headed piston type swash plate compressors using single-headed pistons and double-headed piston type swash plate compressors using double-headed pistons.
An object of the present invention is to provide a lighter swash plate compressor.
According to the present invention, there is provided a swash plate compressor provided with a housing internally defining and forming cylinder bores, a crank chamber, a suction chamber, and a discharge chamber; piston accommodated in each cylinder bore to be able to reciprocate therein; a drive shaft driven by an external drive source and supported by the housing; a swash plate synchronously rotatably supported with respect to the drive shaft; and a pair of shoes provided at the front and rear of the swash plate for connectingly driving the pistons; wherein the shoes are mainly comprised of a magnesium-based material.
Preferably, each shoe is comprised of a shoe substrate comprised of a magnesium-based material and a coating formed on the surface of the shoe substrate for improving the slidability.
Alternatively, each shoe is comprised of a shoe substrate comprised of a magnesium-based material and a coating formed on the surface of the shoe substrate for improving the slidability, and the inclination angle of the variable swash plate is variable with respect to the drive shaft and the pressure in the crank chamber can be adjusted by a control valve to change the inclination angle and adjust the discharge capacity.
Alternatively, each shoe is comprised of a shoe substrate comprised of a magnesium-based material and a coating formed on the surface of the shoe substrate for improving the slidability; the inclination angle of the swash plate is variable with respect to the drive shaft and the pressure in the crank chamber can be adjusted by a control valve to change the inclination angle and adjust the discharge capacity; and the piston is a single-headed piston having a head at only one of the front and rear of the swash plate.